What borer treatment costs, and what you're paying for

What you're actually paying for

Two things: the area of timber, and the access. Treating an open subfloor is straightforward; treating framing behind linings, or joinery that's been painted, takes considerably longer for the same square metreage.

• How much timber is affected, and how accessible it is
• Bare timber (borate application) versus finished timber (pressure injection through the flight holes)
• Whether the damage is confined or spread across the structure
• Whether a full inspection is needed first to work out which species you have

Why the cheapest option usually isn't

A borer larva sits inside the timber for three to five years before it emerges. Any treatment that breaks down faster than that clears the generation currently near the surface and leaves everything deeper in the wood untouched.

That's the case for borate powders: they diffuse into the wood and don't break down over time, so the protection outlasts the life cycle. A cheaper, shorter-lived surface treatment means paying again inside a few years, on timber that's had more time to be eaten.

Get it identified first

Three different insects attack New Zealand building timber and they don't all need the same treatment. Paying to treat borer when what you have is drywood termite or two-toothed longhorn is money spent on the wrong problem. Identification comes before a quote.